In the recording method by means of an inkjet printer which is one of the typical methods among various color recording methods, various methods for discharging ink have been developed. In any of the methods, ink droplets are generated and adhered onto various record-receiving materials (such as paper, film and cloth) to perform recording. This has been rapidly prevailing lately and is expected to continue growing remarkably in the future because of features such as quietness without noise generation due to no direct contact of a recording head with a record-receiving material and as easiness in downsizing, speedup and colorization.
Conventionally, as an ink for fountain pens, felt-tip pens or the like and as an ink for inkjet recording, water-based inks where a water-soluble dye is dissolved in an aqueous medium have been used. In these water-based inks, a water-soluble organic solvent is generally added to prevent ink from clogging at a pen tip or an inkjet nozzle. These conventional inks are required to provide recorded images with sufficient density, not to clog at a pen tip or a nozzle, to dry quickly on a record-receiving material, to bleed less, to have an excellent storage stability, and so on. In addition, recorded images formed are required to have fastnesses such as water fastness, light fastness and moisture fastness.
Meanwhile, images or character information on color displays of computers are generally expressed by subtractive color mixing of 4 primary color inks of yellow (Y), magenta (M), cyan (C) and black (K) for color recording by an ink jet printer. In order that the hues of an image expressed by additive color mixing of red (R), green (G) and blue (B) on CRT displays and the like is reproduced, as faithfully as possible, with images expressed by subtractive color mixing, it is desired that each of Y, M and C has a hue as close to each standard as possible and also is vivid. In addition, it is required that ink compositions to be used for them are stable in storage for a long period of time, and that images printed therewith have a high concentration and said images are excellent in fastnesses such as water fastness, light fastness, and gas fastness.
The application of inkjet printers has been widely spread in the fields ranging from small printers for office automation to large printers for industrial use, and therefore fastnesses such as water fastness, moisture fastness, light fastness and gas fastness have been required more than ever. Water fastness has been largely improved by coating organic or inorganic particulates of porous silica, cation polymer, aluminasol, special ceramic and the like together with a PVA resin on a paper surface to provide an image receiving layer on a record-receiving material. “Moisture fastness” means durability against a phenomenon that the dye in a record-receiving material bleeds around the colored image when the colored record-receiving material is stored under an atmosphere of high humidity. Dye bleeding extremely deteriorates image quality in images particularly required to have a high resolution and photo-like image quality, and therefore it is important to reduce such bleeding as far as possible. As for light fastness, technique for large improvement thereof has not established yet. In particular, many of coloring matters for magenta among 4 primary colors of Y, M, C and K originally have low light fastness, and therefore improvement thereof is an important problem. In addition, there are more opportunities to print pictures at home with recent spread of digital cameras, and image discoloration by oxidizing gases such as ozone gas and nitrogen oxides in the air where printed matters obtained are stored is acknowledged as a problem. Oxidizing gas has a nature to react with dyes on or in a recorded paper, causing discoloration or fading of the printed image. Among oxidizing gasses, ozone gas is regarded as a main causative agent accelerating color-fading phenomenon of inkjet-recorded images. This phenomenon of discoloration or fading is characteristic of inkjet images, and therefore improvement of ozone gas fastness is an important problem as well as improvement of light fastness.
As a magenta coloring matter used in water-soluble inks for inkjet recording, typical are xanthene based coloring matters and azo based coloring matters using H acid (1-amino-8-hydroxy-naphthalene-3,6-disulfonic acid). However, the former is very excellent in hue and vividness but very inferior in light fastness. On the other hand, in the latter, some are good in terms of hue and water fastness, but many are inferior in light fastness and vividness. In addition, as for this type, a magenta dye relatively excellent in vividness and light fastness has been developed but it still has a low level in light fastness compared with dyes having a different hue such as a cyan dye represented by a copper phthalocyanine-based coloring matter and a yellow dye.
Examples of a coloring matter for magenta excellent in vividness and light fastness include an anthrapyridone-based coloring matter (see, for example, Patent Literatures 1 to 11), but a coloring matter for magenta satisfying all of hue, vividness, light fastness, moisture fastness, gas fastness and dissolving stability has yet to be obtained.    Patent Literature 1: JP H10-306221 A (pp. 1 to 3 and 7 to 18)    Patent Literature 2: JP 2000-109464 A (pp. 1 to 2 and 8 to 12)    Patent Literature 3: JP 2000-169776 A (pp. 1 to 2 and 6 to 9)    Patent Literature 4: JP 2000-191660 A (pp. 1 to 3 and 11 to 14)    Patent Literature 5: JP 2000-256587 A (pp. 1 to 3 and 7 to 18)    Patent Literature 6: JP 2001-72884 A (pp. 1 to 2 and 8 to 11)    Patent Literature 7: JP 2001-139836 A (pp. 1 to 2 and 7 to 12)    Patent Literature 8: WO 2004/104108 A1 (pp. 20 to 36)    Patent Literature 9: JP 2003-192930 A (pp. 1 to 4 and 15 to 18)    Patent Literature 10: JP 2005-8868 A (pp. 1 to 3 and 15 to 22)    Patent Literature 11: JP 2005-314514 A (pp. 1 to 3 and 15 to 20)